With electronic signal switching speeds currently in the gigahertz range and still increasing, the mechanical technology employed to route high-speed signals around an electronic system has struggled to keep pace. The task of routing these signals by way of cables between different printed circuit boards (PCBs) has been especially troublesome. Generally speaking, standard PCB cable connectors have been used to attach signal wires to PCBs. However, in some applications, such connectors cause problems that are exacerbated by the switching speeds of electronic signals encountered today.
For example, as shown in FIG. 1, the task of probing signals in an electronic system today with test equipment, such as oscilloscopes and logic analyzers, oftentimes requires the use of a PCB connector 100 to attach coaxial test equipment probes 110 to a target circuit card 120 containing the signal lines to be probed. Termination circuits (not shown in FIG. 1) are typically employed within a probe cable connector housing 130 so that the operation of the signals under test are not adversely affected by the transmission line stubs formed by the probes. Unfortunately, the use of connectors creates at least two problems in such applications. First, the probe termination circuits, being resident in cable connector housing 130, are typically located several millimeters away from the point at which probes 110 couple with the signals under test on target circuit board 120, due to the length of the conductive material required to traverse the connector. As shown in FIG. 2, which is a schematic representation of the connector configuration of FIG. 1, a transmission line stub 200 exists between termination circuit 210 (comprising a parallel configuration of a resistor R1 and a capacitor C1) and the probed signal on target circuit board 120. The faster the switching speed of the signal under test, the more that transmission line stub 200 will affect the signal""s operation by way of unwanted signal reflections. Second, PCB connector 100 (of FIG. 1) occupies valuable board space that could be allocated to other functional circuitry. This space consideration becomes an important issue as the functional capacity of integrated circuits (ICs) continues to increase, making each square inch on target circuit board 120 capable of holding even more circuitry than before.
As a result, the use of a connection structure for attaching signal wires to a PCB that reduces the amount of board space allocated to that structure on the PCB, as well as allows any necessary termination circuits to be located close to the PCB, would be advantageous. Such a device would be desirable for high-speed, high-density applications, such as, for example, circuit probing with oscilloscopes and logic analyzers, due to the associated improvements in target board space efficiency and signal integrity.
Specific embodiments according to the present invention, to be described herein, provide an effective structure for coupling a signal wire and associated termination circuit to a target printed circuit board without the use of a standard connector configuration. An electrical circuit substrate, capable of carrying components and connecting them to other signal wires, is attached perpendicularly to the target circuit board using solder for electrical connectivity and mechanical stability. The termination circuit, electrically coupled to both the signal wire and the target circuit board, resides on the electrical circuit substrate near the end that is coupled with the target circuit board. This positioning is employed to minimize the distance between the termination circuit and the signal on the target circuit board to which the termination circuit is connected. Specific embodiments of the invention involve the use of a rigid circuit board or a flex circuit as the electrical circuit substrate.
Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.